Regular Expression Matching and Operational Semantics

Many programming languages and tools, ranging from grep to the Java String library, contain regular expression matchers. Rather than first translating a regular expression into a deterministic finite automaton, such implementations typically match the regular expression on the fly. Thus they can be seen as virtual machines interpreting the regular expression much as if it were a program with some non-deterministic constructs such as the Kleene star. We formalize this implementation technique for regular expression matching using operational semantics. Specifically, we derive a series of abstract machines, moving from the abstract definition of matching to increasingly realistic machines. First a continuation is added to the operational semantics to describe what remains to be matched after the current expression. Next, we represent the expression as a data structure using pointers, which enables redundant searches to be eliminated via testing for pointer equality. From there, we arrive both at Thompson's lockstep construction and a machine that performs some operations in parallel, suitable for implementation on a large number of cores, such as a GPU. We formalize the parallel machine using process algebra and report some preliminary experiments with an implementation on a graphics processor using CUDA.Comment: In Proceedings SOS 2011, arXiv:1108.279

Theoretical values of convective turnover times and Rossby numbers for solar-like, pre-main sequence stars

Magnetic fields are at the heart of the observed stellar activity in late-type stars, and they are presumably generated by a dynamo mechanism at the interface layer between the radiative and the convective stellar regions. Since dynamo models are based on the interaction between differential rotation and convective motions, the introduction of rotation in the ATON 2.3 stellar code allows for explorations regarding a physically consistent treatment of magnetic effects in stellar structure and evolution, even though there are formidable mathematical and numerical challenges involved. As examples, we present theoretical estimates for both the local (tau_c) and global (tau_g) convective turnover times for rotating pre-main sequence solar-type stars, based on up-to-date input physics for stellar models. Our theoretical predictions are compared with the previous ones available in the literature. In addition, we investigate the dependence of the convective turnover time on convection regimes, the presence of rotation and atmospheric treatment. Those estimates, this quantities can be used to calculate the Rossby number, Ro, which is related to the magnetic activity strength in dynamo theories and, at least for main-sequence stars, shows an observational correlation with stellar activity. More important, they can also contribute for testing stellar models against observations. Our theoretical values of tau_c, tau_g and Ro qualitatively agree with those published by Kim & Demarque (1996). By increasing the convection efficiency, tau_g decreases for a given mass. FST models show still lower values. The presence of rotation shifts tau_g towards slightly higher values when compared with non-rotating models. The use of non-gray boundary conditions in the models yields values of tau_g smaller than in the gray approximation.Comment: 10 pages, 14 figures, accepted for publication in A&

Cutting out continuations

In the field of program transformation, one often transforms programs into continuation-passing style to make their flow of control explicit, and then immediately removes the resulting continuations using defunctionalisation to make the programs first-order. In this article, we show how these two transformations can be fused together into a single transformation step that cuts out the need to first introduce and then eliminate continuations. Our approach is calculational, uses standard equational reasoning techniques, and is widely applicable

Absence of correlation between built-in electric dipole moment and quantum Stark effect in InAs/GaAs self-assembled quantum dots

We report significant deviations from the usual quadratic dependence of the ground state interband transition energy on applied electric fields in InAs/GaAs self-assembled quantum dots. In particular, we show that conventional second-order perturbation theory fails to correctly describe the Stark shift for electric field below $F = 10$ kV/cm in high dots. Eight-band ${\bf k}\cdot{\bf p}$ calculations demonstrate this effect is predominantly due to the three-dimensional strain field distribution which for various dot shapes and stoichiometric compositions drastically affects the hole ground state. Our conclusions are supported by two independent experiments.Comment: 4 pages, 4 figure

Young pre-Low-Mass X-ray Binaries in propeller phase : Nature of the 6.7-hour periodic X-ray source 1E 161348-5055 in RCW 103

Discovery of the 6.7-hour periodicity in the X-ray source 1E 161348-5055 in RCW 103 has led to investigations of the nature of this periodicity. We explore a model for 1E 161348-5055, wherein a fast-spinning neutron star with a magnetic field $\sim 10^{12}$ G in a young pre-Low-Mass X-ray Binary (pre-LMXB) with an eccentric orbit of period 6.7 hr operates in the "propeller" phase. The 6.7-hr light curve of 1E 161348-5055 can be quantitatively accounted by a model of orbitally-modulated mass transfer through a viscous accretion disk and subsequent propeller emission (both Illarionov-Sunyaev type and Romanova-Lovelace et al type), and spectral and other properties are also in agreement. Formation and evolution of model systems are shown to be in accordance both with standard theories.Comment: 11 pages, 4 figures, accepted for publication in Astronomy and Astrophysics on 23/08/200

Time-resolved spectroscopy of multi-excitonic decay in an InAs quantum dot

The multi-excitonic decay process in a single InAs quantum dot is studied through high-resolution time-resolved spectroscopy. A cascaded emission sequence involving three spectral lines is seen that is described well over a wide range of pump powers by a simple model. The measured biexcitonic decay rate is about 1.5 times the single-exciton decay rate. This ratio suggests the presence of selection rules, as well as a significant effect of the Coulomb interaction on the biexcitonic wavefunction.Comment: one typo fixe

Exploiting exciton-exciton interactions in semiconductor quantum dots for quantum-information processing

We propose an all-optical implementation of quantum-information processing in semiconductor quantum dots, where electron-hole excitations (excitons) serve as the computational degrees of freedom (qubits). We show that the strong dot confinement leads to an overall enhancement of Coulomb correlations and to a strong renormalization of the excitonic states, which can be exploited for performing conditional and unconditional qubit operations.Comment: 5 pages revtex, 2 encapsulated postscript figures. Accepted for publication in Phys. Rev. B (Rapid Communication

Antibodies to the Mr 64,000 (64K) protein in islet cell antibody positive non-diabetic individuals indicate high risk for impaired Beta-cell function

A prospective study of a normal childhood population identified 44 islet cell antibody positive individuals. These subjects were typed for HLA DR and DQ alleles and investigated for the presence of antibodies to the Mr 64,000 (64K) islet cell antigen, complement-fixing islet cell antibodies and radiobinding insulin autoantibodies to determine their potency in detecting subjects with impaired Beta-cell function. At initial testing 64K antibodies were found in six of 44 islet cell antibody positive subjects (13.6%). The same sera were also positive for complement-fixing islet cell antibodies and five of them had insulin autoantibodies. During the follow-up at 18 months, islet cell antibodies remained detectable in 50% of the subjects studied. In all six cases who were originally positive, 64K antibodies were persistently detectable, whereas complement-fixing islet cell antibodies became negative in two of six and insulin autoantibodies in one of five individuals. HLA DR4 (p < 0.005) and absence of asparic acid (Asp) at position 57 of the HLA DQ chain (p < 0.05) were significantly increased in subjects with 64K antibodies compared with control subjects. Of 40 individuals tested in the intravenous glucose tolerance test, three had a first phase insulin response below the first percentile of normal control subjects. Two children developed Type 1 (insulin-dependent) diabetes mellitus after 18 and 26 months, respectively. Each of these subjects was non-Asp homozygous and had persistent islet cell and 64K antibodies. We conclude that 64K antibodies, complement-fixing islet cell antibodies and insulin autoantibodies represent sensitive serological markers in assessing high risk for a progression to Type 1 diabetes in islet cell antibody positive non-diabetic individuals

Стан соснових насаджень на водно-льодовикових відкладах у Житомирському поліссі

The results of researches of the state of forest plantations of pine trees of different ages on water-glacial deposits in Zhytomyr Polissya are presented. The phyto-indicative analysis describes the types of forest conditions, such as: fresh bory and fresh subory. It is established that about 40&nbsp;% of trees grow in fresh bory by the first class of Kraft and in fresh subory&nbsp;– about 50&nbsp;%. The first class of merchantability includes 30&nbsp;% of trees in fresh bory and 47&nbsp;% of trees from their total number in fresh subory. The number of weakened, dying and dead trees in fresh bory is 35.5&nbsp;%, and in fresh subory 54.3&nbsp;%. The dying and dead trees appear as a result of diseases, insect pests and competition for nutrients. It is found out that the absolute value of the annual tree rings decreases with the increase in the age of pine: in fresh bory by 28.0&nbsp;%, in fresh subory by 50.5&nbsp;%. It is established that the least annual rings are characteristic for plantations of fresh bory, and the widest ones&nbsp;– for tree stands growing in richer conditions (fresh subory). The maximum values of the growth of annual rings are recorded for mature and overmature forest stands, regardless of forest conditions. By dendrochronological analysis it is established that the annual radial increment of the pine varies between 1.19–3.94&nbsp;mm. By the values of the standard deviation it is clear that the organization of the system continues in the fresh bory throughout the studied period, and in the fresh subory&nbsp;– the system is formed at the age of up to 40&nbsp;years. By the values of the coefficients of variation, the structural stability of plantations on water-glacial deposits decreases with age. It is established that identical or similar coefficients of variation are recorded in all age groups. Thus, all this time the proportion of anomalous components of radial growth increases, the plantations are structurally unstable and more vulnerable to environmental factors. According to that it can be asserted that in fresh bory, in fact, stable, internally balanced Scots pine stands are not formed in practice, while in fresh subory pine stands are organized in a single phytosystem only after 60&nbsp;years.Наведено результати досліджень стану лісових насаджень сосни звичайної різного віку на водно-льодовикових відкладах у Житомирському Поліссі. За фітоіндикаційним аналізом охарактеризовано типи лісорослинних умов як свіжі бори та свіжі субори. Встановлено, що у свіжих борах за І класом Крафта ростуть близько 40&nbsp;% дерев, а у свіжих суборах&nbsp;– близько 50&nbsp;%. До І класу товарності належить 30&nbsp;% дерев у свіжих борах та 47&nbsp;% дерев від загальної їх кількості у свіжих суборах. Частка ослаблих, всихаючих і відмерлих дерев у свіжих борах становить 35,5&nbsp;%, а у свіжих суборах&nbsp;– 54,3&nbsp;%. Виявлено, що абсолютні значення величин річних кілець дерев зменшуються із збільшенням віку сосни звичайної: у свіжих борах&nbsp;– на 28,0&nbsp;%, у свіжих суборах&nbsp;– на 50,5&nbsp;%. Встановлено, що найвужчі річні кільця характерні для насаджень свіжих борів, а найширші&nbsp;– для деревостанів, що ростуть у багатших умовах (свіжий субір). Максимальні значення приросту річних кілець зареєстровано для стиглих та перестійних деревостанів, незалежно від лісорослинних умов. Щорічний радіальний приріст сосни звичайної змінюється у межах 1,19–3,94&nbsp;мм. За розрахунковими значеннями стандартного відхилення та коефіцієнта варіації можна стверджувати, що у свіжих борах фактично не формуються стійкі, внутрішньо збалансовані деревостани сосни звичайної, а у свіжих суборах соснові деревостани організовуються в єдину фітосистему лише після 60-ти років

Optical excitations of a self assembled artificial ion

By use of magneto-photoluminescence spectroscopy we demonstrate bias controlled single-electron charging of a single quantum dot. Neutral, single, and double charged excitons are identified in the optical spectra. At high magnetic fields one Zeeman component of the single charged exciton is found to be quenched, which is attributed to the competing effects of tunneling and spin-flip processes. Our experimental data are in good agreement with theoretical model calculations for situations where the spatial extent of the hole wave functions is smaller as compared to the electron wave functions.Comment: to be published in Physical Review B (rapid communication